The present invention relates to sports racquets, for example tennis, squash, badminton, and racquetball racquets. Such racquets have a head portion containing an interwoven string bed, a handle, and a shaft portion connecting the head portion to the handle.
In conventional racquets, holes for anchoring the ends of the strings are formed in the frame by drilling small string holes in the frame after the racquet is molded. Generally, each string hole accommodates a single string. Plastic grommet pegs, which are formed on grommet and bumper strips that extend along the outside surface of the frame, extend through the string holes to protect the strings from the sharp edges of the drilled holes.
Co-owned PCT application WO 2004/075996 discloses a sports racquet in which some adjacent pairs of small string holes along the sides, tip, and throat bridge of the racquet are replaced by enlarged string holes having two inwardly facing string bearing surfaces which are spaced apart by a distance corresponding to the distance between two contiguous main strings or cross strings (referred to herein as “string ports holes”). Preferably the frame is formed of a double tube of carbon fiber-reinforced composite material (a so-called graphite frame), in which the string port holes are molded into as the racquet as the racquet is pressure molded. As a result of using two tubes, each forming one-half of the enlarged string hole, the string holes can have rounded edges and do not require the use of grommet pegs or strips. Also, in the regions between string holes, the adjoining walls of the two tubes are fused together to form a stiffening wall inside the frame. The result is a racquet which has improved torsional stiffness and lighter weight.
The racquet is made in a mold having a mold cavity in the desired shape of the frame. The mold has two halves. A prepreg tube containing an inflatable bladder is placed in each mold half. A plurality of mold insert members, having an outside surface in the desired shape of the string port holes, as well as a plurality of pins to form conventional string holes, are positioned between the two prepreg tubes and the mold is closed. The bladders are then inflated while the mold is heated to cure the composite resin. After removing the racquet frame from the mold, the mold insert members and pins are removed leaving string port holes and conventional string holes, respectively.
It is possible to form a racquet with string port holes using a single frame tube. For example, the racquet frame can be molded from a single prepreg tube, with the holes being drilled after molding. However, drilling string holes, and particularly large string holes such as string port holes, weakens the frame. Alternatively, it is possible to construct the frame by molding two frame halves separately, and then joining the two halves, e.g., by gluing, welding, fusing, or electro-fusing. However, it would be desirable to employ improved methods of forming a racquet frame having port string holes and which is formed from a single frame tube.